ABSTRACTTile Index - Orthophotos of Allegheny County, Pennsylvania - An orthoimage is remotely sensed image data that has been positionally corrected for camera lens distortion, vertical displacement and variations in aircraft altitude and orientation. Orthoimagery combines the image characteristics of a photograph with the geometric qualities of a map. Aerial survey of Allegheny County,Pennsylvania. Orthophotos serve a variety of purposes, from interim maps to field references for earth science investigations and analysis. The digital orthophoto is useful as a layer of a geographic information system and as a tool for revision of digital line graphs and topographic maps.